1. Field of the Invention
The present invention relates to apparatus and methods for testing the depth of structures such as foundations using parallel seismic testing with a cone penetrometer to house the receiving element.
2. Description of the Prior Art
Parallel Seismic (PS) testing has been employed for such uses as determining the depth of an unknown foundation when the foundation top is not accessible or when the piles are too long and slender to be tested by echo techniques. Typically a borehole is drilled into the soil adjacent to the foundation, and the borehole is cased. In the case where the receiver is a hydrophone, the cased borehole is filled with water. In the case where the receiver is a geophone, several geophone receiver components are spaced apart in the borehole.
An exposed portion of the foundation is then impacted with a hammer or the like, and compression or flexural waves travel down the foundation and are transmitted into the surrounding soil. The receiver detects the transmitted signals. The depth of the foundation is indicated by a weaker and slower signal arrival below the tip of the foundation.
Parallel seismic testing is expensive and time consuming because the borehole must be drilled and cased (or at least braced in the case of a geophone receiver).
Cone penetrometers have been used to test soil conditions. For example, Hogentogler & Co., Inc. builds a variety of commercially available cone penetrometer testers (CPTs) such as their Electronic Subtraction Cone CPTs. These units include cone tips each housing a strain gauge transducer and electronics for computing the detected strain and providing it to the user. Tips housing other transducers are also available. The CPT is mounted on a truck or track system, which includes, for example, hydraulic cylinders for driving the CPT cones into the earth.
A need remains in the art for apparatus and methods for doing parallel seismic testing in a quicker, more convenient manner.